|Publication number||US7702077 B2|
|Application number||US 12/122,832|
|Publication date||Apr 20, 2010|
|Filing date||May 19, 2008|
|Priority date||May 19, 2008|
|Also published as||DE102009025841A1, DE102009025841B4, US20090285360|
|Publication number||12122832, 122832, US 7702077 B2, US 7702077B2, US-B2-7702077, US7702077 B2, US7702077B2|
|Inventors||Yang Cao, Louis Paul Inzinna, Richard Michael Roffers, Daniel Qi Tan, Mark E. Vermilyea, Yun Zou|
|Original Assignee||General Electric Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Non-Patent Citations (2), Classifications (7), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The invention relates generally to x-ray tubes and, more particularly, to an apparatus and method of fabricating a high-voltage insulator for x-ray tubes. The invention is described with respect to an x-ray system, but one skilled in the art will recognize that the invention may be used in, for instance, electron tubes or other devices in which high voltage instability occurs.
X-ray systems typically include an x-ray tube, a detector, and a gantry to support the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in a computed tomography (CT) package scanner.
X-ray tubes include a rotating anode structure for the purpose of distributing heat generated at a focal spot. The anode is typically rotated by an induction motor having a cylindrical rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. The rotor of the rotating anode assembly is driven by the stator. An x-ray tube cathode provides a focused electron beam that is accelerated across a cathode-to-anode vacuum gap and produces x-rays upon impact with the anode. Because of the high temperatures generated when the electron beam strikes the target, it is necessary to rotate the anode assembly at high rotational speed.
Newer generation x-ray tubes have increasing demands for providing higher peak power and higher accelerating voltages. For instance, x-ray tubes used in medical applications typically operate at 140 kV or more, while 200 kV or more is common for x-ray tubes used in security applications. However, one skilled in the art will recognize that the invention is not limited to these voltages, and applications requiring greater than 200 kV may be equally applicable. At these voltages, x-ray tubes are susceptible to high-voltage instability and insulator surface flashover which can reduce the life expectancy of the x-ray tube or interfere with the operation of the imaging system.
In a typical x-ray tube, there is a disk-shaped ceramic insulator having an opening for electrical feeds therein. The cathode post, or conduit for the electrical feeds, typically houses three or more electrical leads for feeding voltage to the cathode. Typically, the insulator, at its center opening, is attached to the cathode post which may structurally support the cathode. The cathode typically includes one or more tungsten filaments. At its perimeter, the insulator is typically hermetically connected to a cylindrical frame, which houses a vacuum chamber in which the anode and the cathode are typically positioned. In a monopolar design, voltage may be applied solely to the cathode, or to the anode. By contrast, in a bipolar design, the voltage may be applied to both the anode and cathode.
In either case, areas of the x-ray tube susceptible to failure due to high-voltage stresses include the junctions between the insulator and center cathode support structure, and between the insulator and cylindrical frame. These areas are common sources of the high-voltage instability that can reduce the life expectancy of the x-ray tube and interfere with operation of an imaging system.
The electron beam in the vacuum gap of the x-ray tube creates an electric field therein. There is the potential for insulator surface flashover in an x-ray tube when the intensity of the electric field at the insulator surface causes electrical arcing along the insulator surface between, for example, the cathode post and the cylindrical frame. The intensity of the electric field along the insulator surface, and similarly the likelihood of surface flashover, is highest when electric field force lines are perpendicular to the insulator surface.
In addition to their high-voltage operation, x-ray tubes typically operate at high temperature, which can add to the electrical stresses on x-ray tube insulators. Furthermore, the peak voltages and temperatures to which these components are subjected are likely to increase in future x-ray tube designs. Thermal stresses on x-ray tube components play a role in reducing the life expectancy of the x-ray tube as well. In some advanced applications, x-ray tubes may employ external cooling systems to cool critical components (e.g. the anode). Such advanced applications would benefit from an insulator that enables the flow of coolant to thermally stressed components in the x-ray tube.
Computed tomography (CT) systems represent an advanced application of x-ray tube technology. Some newer generation CT systems rotate the CT gantry, which includes the x-ray tube, about the patient at three revolutions per second or more. Such operation subjects the x-ray tube components to accelerations of 20 g or more, and future applications may exceed 60 g. Additionally, the newer generation CT systems seek to improve performance while decreasing the size and weight of the x-ray tubes. By reducing the size and weight of the devices that are attached to the CT gantry, the mechanical stresses on the gantry and its components are thereby reduced.
Furthermore, future x-ray tube applications may include an increased number of electrical feeds to the cathode to provide additional functionality at the cathode, such as in deflected beam applications.
Therefore, it would be desirable to have an apparatus and method to fabricate an insulator for x-ray or electron tubes that is resistant to high-voltage instability and insulator surface flashover, compact for advanced applications, and modular in design to allow for ease of repair and passage of additional electrical feeds and coolant therein.
The invention provides an apparatus and method for assembling a compact insulator having improved voltage stability.
According to one aspect of the invention, a modular insulator assembly for an x-ray tube includes an annular insulator having a cylindrical perimeter wall, the insulator constructed of an electrically insulative material. A wall member is fixedly attached to and extending beyond the cylindrical perimeter wall, and a first shield positioned adjacent to the wall member and having an end extending proximate a corner formed by the wall member and the insulator.
In accordance with another aspect of the invention, a method of fabricating an x-ray tube includes providing an x-ray-tube frame configured to enclose a vacuum region, and providing an electrical insulator having a perimeter wall. The method further includes attaching a wall member to the perimeter wall, the wall member having a surface exposed to the vacuum region, wherein a confluence of the insulator, the wall surface and the vacuum region form a junction, and positioning one end of a first shield proximately to the junction.
Yet another aspect of the invention includes an imaging system having an x-ray detector and an x-ray tube. The x-ray tube includes an annular insulator having an outer perimeter wall and an inner perimeter wall, a cylindrical wall member attached to the outer perimeter wall, the wall member having a center axis and configured to encircle a vacuum region about the center axis, and wherein a confluence of the insulator, the wall member, and the vacuum region form a first junction, and a first shield having a conical portion and a toroidal portion, wherein a base of the conical portion is attached to the wall member, and wherein the toroidal portion is positioned in the vacuum region between the wall member and the center axis.
Various other features and advantages of the invention will be made apparent from the following detailed description and the drawings.
The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention.
In the drawings:
As shown in
A processor 20 receives the analog electrical signals from the detector 18 and generates an image corresponding to the object 16 being scanned. A computer 22 communicates with processor 20 to enable an operator, using operator console 24, to control the scanning parameters and to view the generated image. That is, operator console 24 includes some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus that allows an operator to control the x-ray system 10 and view the reconstructed image or other data from computer 22 on a display unit 26. Additionally, console 24 allows an operator to store the generated image in a storage device 28 which may include hard drives, floppy discs, compact discs, etc. The operator may also use console 24 to provide commands and instructions to computer 22 for controlling a source controller 30 that provides power and timing signals to x-ray source 12.
Moreover, the invention will be described with respect to use in an x-ray tube. However, one skilled in the art will further appreciate that the invention is equally applicable for other systems (e.g., electron tubes) that require the installation of an electrical insulator that operates under high voltage, having a propensity to experience surface flashover or voltage instability.
The cathode 60 typically includes one or more filaments 55. The cathode filaments 55 are powered by electrical leads 71 that pass through a center post 68 in the vacuum region 54. In addition to electrical leads 71, the center post 68, in an embodiment of the invention, contains coolant lines 185 (in
In operation, an electric current is applied to the desired filament 55 via electrical contacts 77 to heat the filament so that electrons may be emitted from filament 55. A high-voltage electric potential is applied between the anode 56 and the cathode 60, and the difference therebetween results in an electron beam, or electrical current, flowing through the vacuum region 54 from cathode 60 to anode 56. The voltage difference between the anode 56 and the cathode 60 can be maintained using either a monopolar or a bipolar x-ray tube design. For monopolar, the voltage is applied to either the anode 56 or the cathode 60. For bipolar, the voltage is applied to both anode 56 and cathode 60. Depending on the design, high-voltage insulation may be needed at either the anode 56, the cathode 60, or at both locations 56, 60.
The electrons impact the target track material 86 at focal point 61 and x-rays 15 emit therefrom. The x-rays 15 emit through the radiation emission passage 52 toward a detector array, such as detector 18 of
Though the embodiments disclosed show an insulator 73 assembled to the cathode 60 side of the x-ray tube 12, one skilled in the art will be able to envision embodiments in which the anode 56 is at some electric potential, thereby requiring an insulator 73 to be assembled to the anode 56 side of the x-ray tube 12.
During operation of the x-ray tube 12, an electric field is generated within the vacuum region 54 of x-ray tube 12 by the electrical potential between cathode 60 and anode 56. As shown in
Another factor in the initiation of insulator surface flashover typically includes electrons being emitted from the triple-point junctions 160, 161. These electrons gain kinetic energy from the electric field at the insulator surface 180 and cause the electrons to cascade along the insulator surface 180. Electrons with high kinetic energy may strike the insulator surface 180 and produce more electrons through secondary electron emission avalanche. Continuation of this process may lead to electrical breakdown of the insulator 73 at the surface 180.
As explained above, the electric field in the vacuum region 54 is enhanced at the triple-point junctions 160, 161. Such enhancement can lead to electrical-stress-induced failure of the insulator 73 at the triple-point junctions 160, 161, and to voltage instability due to insulator surface flashover during operation of the x-ray tube 12. The likelihood of surface flashover may be reduced, according to embodiments of the invention, by reducing the electron emission at the triple-point junction and by reducing the tangential electric field along the insulator surface 180 such that the field-emitted electrons from the triple-point junction 160, 161 do not gain enough kinetic energy to initiate insulator surface flashover.
A shield 174, having a lip 193 and a cylindrical section 191, is attached to a flange 176. The flange 176 has a small stepped portion 194 machined out of the flange surface. The lip 193 of shield 174 fits into the stepped portion 194 during assembly which serves to electrically couple the shield 174 to the flange 176. When the metal flange 176 is attached to the metal x-ray tube frame 50, the shield 174, flange 176, and frame 50 are all electrically coupled. In embodiments where the cathode 60 is at potential, the x-ray tube frame 50 is typically grounded, in which case the shield 174 is grounded also. The cylindrical section 191 of shield 174 extends along the wall member 170. A roughly U-shaped cavity or groove 215 is formed in insulator 73 near outer perimeter wall 87 such that cavity 215 is formed between the wall member 170 and the insulator 73. Shield 174 has an end 190 that is preferably positioned so that end 190 extends into the cavity 215 and proximate to the triple-point junction 160, thus reducing the electric field intensity at the triple-point junction 160 and improving the high-voltage stability of the x-ray tube 12. As a result, electrical stresses on the insulator 73 at the triple-point junction 160 are also reduced.
As shown in
The flange 176 has a small stepped portion 194 machined out of the flange surface. The lip 195 of shield 175 fits into the stepped portion 194 of flange 176 over the lip 193 of shield 174. A gasket 188, typically made of a malleable metal such as copper, is used to attach shields 174, 175 to flange 176. The gasket 188 fits over the lips 193, 195 of the two shields 174, 175 and into a second stepped portion 196 machined out of the surface of the flange 176. Assembly in this manner serves to electrically couple the second shield 175 to shield 174, to flange 176, and to the x-ray tube frame 50. Both shield components 174, 175 are made of an electrically conductive material. In preferred embodiments, shields 174, 175 are made of metals that can accept a high polish such as stainless steel, Kovar, Invar, or oxygen-free high-purity copper.
Referring still to
Typically, an embodiment, wherein the cathode 60 is at potential, will have shield 177 at the center post 68 to protect the triple-point junction 161. An embodiment, wherein anode 56 is at potential, will generally have shield 174 at outer wall member 170 to protect the triple-point junction 160. However, it is contemplated that insulator assembly 120 may include one or both of shields 177, 174 to improve the high-voltage stability of x-ray tube 12.
Shields 177 and 174 serve to reduce electron emission at the triple point junctions 160, 161, while shield 175 serves to reduce the tangential electric field at the insulator surface 180 by causing compression of the electric field in the vacuum region 54 to change the direction of the electric field force lines 220 such that the force lines are less perpendicular with respect to the insulator surface 180. The curve of the toroidal portion 202 compresses the electrical field lines 220 at the toroidal portion 202. Because the separation between the field lines 220 increase with distance from the toroidal portion 202, electrical field lines 220 are caused to impinge insulator surface 180 more and more acutely, as illustrated by
Referring again to
Ceramic coatings 150, 151 include simple oxides, such as aluminum oxide and zirconium dioxide, ferroelectric thin films, such as barium titanate, glasses, thermal barrier coatings, and dielectric layers, such as tantalum pentoxide and silicon oxynitride. Ceramic coatings 150, 151 can be applied by various techniques including dip coating, dielectric paste printing, aerosol spraying, plasma spraying, and water-based ceramic paste brushing. Applied coatings generally require drying or curing at temperatures form 100° C. to 600° C. depending on the curing process used.
The combination of two shield components 174, 175 (shown in
A modular design for the insulator assembly 120 may enable some components to be shared between insulator assemblies made for the anode 56, and those made for the cathode 60, while other components may have to be specifically adapted for use at either the anode 56 or cathode 60. This flexibility, which allows use of the same component in different areas of the x-ray tube 12, can make the modular design a more cost-effective method of fabricating insulator assemblies. Also, repairs are more easily and inexpensively performed with a modular design in that, damage to any one part of the insulator assembly may require replacement of only the damaged component while leaving the undamaged portions of the insulator assembly unaffected.
While electron tube design may include various structural incarnations, the underlying principles of operation are essentially the same such that one skilled in the art will understand that the scope of the invention includes application to electron tubes generally as well as the x-ray tubes described herein.
According to one embodiment of the invention, a modular insulator assembly for an x-ray tube includes an annular insulator having a cylindrical perimeter wall, the insulator constructed of an electrically insulative material. A wall member is fixedly attached to and extending beyond the cylindrical perimeter wall, and a first shield positioned adjacent to the wall member and having an end extending proximate a corner formed by the wall member and the insulator.
In accordance with another embodiment of the invention, a method of fabricating an x-ray tube includes providing an x-ray-tube frame configured to enclose a vacuum region, and providing an electrical insulator having a perimeter wall. The method further includes attaching a wall member to the perimeter wall, the wall member having a surface exposed to the vacuum region, wherein a confluence of the insulator, the wall surface and the vacuum region form a junction, and positioning one end of a first shield proximately to the junction.
Yet another embodiment of the invention includes an imaging system having an x-ray detector and an x-ray tube. The x-ray tube includes an annular insulator having an outer perimeter wall and an inner perimeter wall, a cylindrical wall member attached to the outer perimeter wall, the wall member having a center axis and configured to encircle a vacuum region about the center axis, and wherein a confluence of the insulator, the wall member, and the vacuum region form a first junction, and a first shield having a conical portion and a toroidal portion, wherein a base of the conical portion is attached to the wall member, and wherein the toroidal portion is positioned in the vacuum region between the wall member and the center axis.
The invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2291948 *||Jun 27, 1940||Aug 4, 1942||Westinghouse Electric & Mfg Co||High voltage chi-ray tube shield|
|US2559526||Dec 20, 1949||Jul 3, 1951||Research Corp||Anode target for high-voltage highvacuum uniform-field acceleration tube|
|US3517195 *||Jul 2, 1968||Jun 23, 1970||Atomic Energy Commission||High intensity x-ray tube|
|US3626231||Mar 5, 1969||Dec 7, 1971||Sylvania Electric Prod||Thermal shunt for a cathode structure|
|US3737698||Nov 24, 1971||Jun 5, 1973||Carter F||X-ray target changer using a translating anode|
|US3911306 *||Jan 4, 1974||Oct 7, 1975||Philips Corp||High-voltage vacuum tube, notably an X-ray tube, comprising a metal sleeve|
|US4405876||Apr 2, 1981||Sep 20, 1983||Iversen Arthur H||Liquid cooled anode x-ray tubes|
|US4618977 *||Dec 9, 1985||Oct 21, 1986||U.S. Philips Corporation||X-ray tube comprising an at least partly metal housing and an electrode which carries a positive high voltage with respect thereto|
|US4679219 *||Jun 12, 1985||Jul 7, 1987||Kabushiki Kaisha Toshiba||X-ray tube|
|US5056126||Nov 30, 1987||Oct 8, 1991||Medical Electronic Imaging Corporation||Air cooled metal ceramic x-ray tube construction|
|US5122332||Nov 28, 1989||Jun 16, 1992||Virginia Russell||Protecting organisms and the environment from harmful radiation by controlling such radiation and safely disposing of its energy|
|US5268955||Apr 3, 1992||Dec 7, 1993||Picker International, Inc.||Ring tube x-ray source|
|US5402464 *||Sep 28, 1993||Mar 28, 1995||Licentia Patent-Verwaltungs-Gmbh||High-voltage electronic tube|
|US5689542 *||Jun 6, 1996||Nov 18, 1997||Varian Associates, Inc.||X-ray generating apparatus with a heat transfer device|
|US6331194||Jul 8, 1997||Dec 18, 2001||The United States Of America As Represented By The United States Department Of Energy||Process for manufacturing hollow fused-silica insulator cylinder|
|US6351520 *||Dec 4, 1998||Feb 26, 2002||Hamamatsu Photonics K.K.||X-ray tube|
|US6798865 *||Nov 14, 2002||Sep 28, 2004||Ge Medical Systems Global Technology||HV system for a mono-polar CT tube|
|US6819741 *||Mar 3, 2003||Nov 16, 2004||Varian Medical Systems Inc.||Apparatus and method for shaping high voltage potentials on an insulator|
|US7218707 *||Sep 9, 2002||May 15, 2007||Comet Holding Ag||High-voltage vacuum tube|
|US20060185889||Jun 4, 2004||Aug 24, 2006||Koninklijke Philips Electronics N.V.||High voltage insulating materials|
|US20070058782 *||Aug 30, 2006||Mar 15, 2007||Hamamatsu Photonics K.K.||X-ray tube|
|US20070274453||May 23, 2007||Nov 29, 2007||Ronald Dittrich||X-ray radiator with a photocathode irradiated with a deflected laser beam|
|1||"Center for Micro- and Nanotechnologies Annual Report 2004"; Technical University of Ilmenau; 2004; pp. 1-132.|
|2||"Surface and Material Technologies Information Brochure"; European Organization for Nuclear Research; 2000; pp. 1-28.|
|U.S. Classification||378/142, 378/121|
|International Classification||H01J35/06, H01J35/00|
|Cooperative Classification||H01J35/16, H01J2235/0233|
|May 19, 2008||AS||Assignment|
Owner name: GENERAL ELECTRIC COMPANY, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CAO, YANG;INZINNA, LOUIS PAUL;ROFFERS, RICHARD MICHAEL;AND OTHERS;REEL/FRAME:020964/0947;SIGNING DATES FROM 20080505 TO 20080516
Owner name: GENERAL ELECTRIC COMPANY,NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:CAO, YANG;INZINNA, LOUIS PAUL;ROFFERS, RICHARD MICHAEL;AND OTHERS;SIGNING DATES FROM 20080505 TO 20080516;REEL/FRAME:020964/0947
|Nov 29, 2013||REMI||Maintenance fee reminder mailed|
|Apr 20, 2014||LAPS||Lapse for failure to pay maintenance fees|
|Jun 10, 2014||FP||Expired due to failure to pay maintenance fee|
Effective date: 20140420